1. Field of the Invention
The present invention relates to an improved system for forming a fluid tight interface between conduits entering a subsurface chamber for servicing aircraft and the walls of the chamber.
2. Description of the Prior Art
Aircraft docking areas at many air terminals are often provided with subsurface aircraft servicing pits located beneath the tarmac across which the wheels of aircraft roll while the aircraft are on the ground. Subservice aircraft servicing pits have the distinct advantage over mobile land vehicles used to service aircraft in that subsurface aircraft servicing pits do not provide obstacles to docking and departing aircraft and do not interfere with the maneuvering of aircraft in docking and refueling areas.
Conventional subsurface aircraft servicing pits are frequently formed as prefabricated fiberglass enclosures having hinged aluminum or steel access doors and hatches to allow access from above. The access doors are located flush with the surface of the aircraft loading and refueling aprons. Fuel pipes, electrical lines and conduits for supplying heated and cooled air emanate from central supply sources within an air terminal and extend underground beneath aircraft loading and refueling aprons and into subsurface aircraft servicing pits through openings in the walls of the pits.
When fuel pipes are brought into subsurface aircraft servicing pits they are terminated at valves or hydrants within the pits. Since aircraft fuel can be a form of toxic waste, if released into the environment, it is important to seal the subsurface access opening of the pit beneath the ground to prevent any spilled aircraft fuel from migrating out of the pit and into ground water. To this end the openings of aircraft servicing pits are conventionally provided with moisture or ground seals that extend from the walls of the pit to the outer surfaces of the pipes and ducts which enter through openings in the walls of the pit and which terminate within the pit.
Such ground moisture seals also prevent ground water from percolating up through the bottom of the pit or around pipes and ducts entering through openings in the pit. The exclusion of ground water from the chamber defined within the pit aids in preventing corrosion of the terminals and valves housed within the pits and also aids in guarding against short circuits to ground from electrical outlet terminating within the pit.
While conventional ground or moisture seals can be installed in pit openings to provide a fluid tight barrier, once installed such seals remain in position for prolonged periods of time under widely fluctuating weather and temperature conditions. Not infrequently, ground and moisture seals which are initially fluid tight do develop leaks over extended periods of time. Even a small amount of corrosion or contraction at an interface between a duct or conduit and a moisture seal will break the fluid tight barrier that was initially present when the pit was put into service As a result, fuel which may spill or leak from the fueling hydrant can reach the soil beneath the pit through discontinuities in the moisture barrier. Likewise, ground water can enter the pit through such crevices in the sealing system which do develop over periods of time. Since at present there is no way to detect the existence of liquids leaking out of an aircraft servicing pit, such leaks usually remain undetected.